Bioinformatics infrastructural activities are crucial to modern biological research. Complete and up-to-date databases of biological knowledge are vital for the increasingly information-dependent biological and biotechnological research. With the recent accumulation of genome sequences for many organisms, most notably the draft human sequence, attention is now turning to the identification and function of proteins encoded by these genomes. With the increasing volume and variety of protein sequences and functional information, a central database of protein sequence and function will provide a cornerstone for a wide range of scientists active in modern biological research, and here especially in the field of proteomics. Currently, several databases exist with different coverage of protein sequences and with various types of information annotated. A central resource is necessary to ensure that scientists receive rich and non-redundant information at a single location, and this is what the UniProt project wants to achieve by joining the forces of the SWISS-PROT, TrEMBL and PIR protein database activities The broad, long-term objective of the United Protein Databases (UniProt) can be summarized as the creation, maintenance and provision of a stable, comprehensive, fully classified, richly and accurately annotated protein sequence knowledgebase, with extensive cross-references and querying interfaces. The work will be built upon solid foundations laid by the three UniProt consortium members, SWlSS-PROT and TrEMBL at the European Bioinformatics Institute (EBI) and the Swiss Institute of Bioinformatics (SIB), and the Protein Information Resource (PIR) at Georgetown University Medical Center. UniProt will facilitate development of preventive and curative strategies for health maintenance by allowing researchers to integrate the enormous amount of data from the Human Genome Project and from structural and functional genomics and proteomics projects to understand the genetic and biological mechanisms causing human disease.